Setting fixed salt with libscrypt_hash

[Slips-PC]

Title is self explanatory. How can I set a fixed salt in the libscrypt_hash function, for i.e getting a specific salt from the system to check password input against a predetermined hash.

[technion]

This function is described in the README.
int libscrypt_scrypt(const uint8_t *passwd, size_t passwdlen, const uint8_t *salt, size_t saltlen, uint64_t N, uint32_t r, uint32_t p, /*@out@*/ uint8_t *buf, size_t buflen);